Of course it is a warning sign.
Or rather, it is a sign the project is already dead.

I would say that last year, the vast majority of these kinds of projects were not out to scam people.
They just failed miserably due to market conditions and poor management.
Some of them just bail, they will literally disappear.  They are cutting their losses and moving on.
Some of them get desperate and try to do another round of funding.

Whatever the case is, it is a losing situation.
The best thing for you to do is to move on.
Even if you do get paid, the coin will be worthless, so no point in stressing over it.